1. Field of the Invention
The present invention relates to a helical blade type fluid compressor which can be used for compressing refrigerant gas in a refrigeration cycle.
2. Description of the Related Art
A helical blade type compressor is a closed compressors. A compressor of this type is disclosed in U.S. Pat. No. 4,871,304 . The compressor has a compression section which is driven by a motor and arranged in a closed case. The compression section is provided with a cylinder which is rotated together with a rotor in a motor. A piston, having a center axis eccentric to the axis of the cylinder, is rotatably housed in the cylinder. A spiral or helical groove is formed on the outer circumference of the piston in the axial direction. The pitches of the spiral groove are gradually narrowed along the distance of the piston from one end to the other. A blade having appropriate elasticity is fitted into the spiral groove.
A space between the cylinder and the piston is partitioned into a plurality of operating chambers by the blade. The volumes of these operating chambers are gradually decreased along the distance from the suction side to the discharge side of the cylinder. When the cylinder and the piston are rotated in unison by the motor, refrigerant gas in the refrigeration cycle is drawn into the operating chamber through the suction side of the cylinder. The gas thus drawn in is successively fed to the operating chambers located on the discharge side of the cylinder. As the gas is being fed to the operating chambers it is also being compressed in the operating chambers. The gas is then discharged into the closed case through the discharge end of the cylinder.
In the above-described compressor, however, the pressure of the refrigerant gas in the operating chamber located on the discharge side of the cylinder is higher than the pressure of the gas in the operating chamber located on the suction side of the cylinder. The difference in pressure increases the friction between the piston and bearing. Thus a large drive force is needed to rotate the cylinder and piston.
A compressor disclosed in U.S. Pat. No. 5,090,874 is an improvement of the above-mentioned compressor. First and second spiral grooves are formed on the outer circumference of the piston. The first groove extends from the center to one end of the piston while the second groove extends from the center to the other end of the piston. First and second blades are fitted into first and second spiral grooves, respectively. The refrigerant gas that is drawn into the cylinder is introduced into the center portion of piston and separately supplied to the right and left portions of operating chambers. The refrigerant gas is transferred and compressed in two directions which are opposed to each other. Therefore, the thrust forces which act on the piston from both ends to the center of the cylinder cancel each other out.